<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        div{
            position: relative;
            width: 500px;
            height:300px;
            border: 1px solid black;

            -webkit-border-radius: 50%;    /* 兼容谷歌浏览器*/
            -moz-border-radius: 50%;    /*兼容火狐浏览器*/
            border-radius: 50%;
            font-size: 24px;
            font-weight: bold;
            text-align: center;
            line-height: 300px;

        }
        div:before,div:after{
            position: absolute;
            content: "";
            display: block;
            border: 1px solid black;
            border-radius: 50%;
        }
        div:before{
            width: 50px;
            height: 50px;
            bottom: -25px;
            right: 0px;
        }
        div:after{
            width: 20px;
            height: 20px;
            bottom: -50px;
            right: -25px;
        }
    </style>
</head>
<body>


<div>大家好，欢迎来到慕课网</div>
</body>
</html>